This invention relates generally to the field of disc drive data handling systems, and more particularly, but not by way of limitation, to a method and apparatus for reducing read element power dissipation during a disc drive write operation to improve operational life of the read element.
Disc drives are data handling systems used to magnetically store and retrieve digital data files. A typical disc drive comprises one or more rigid recording storage discs arranged about a spindle motor for rotation at a constant high speed. A corresponding array of read/write heads are provided to transfer data between tracks defined on the disc surfaces and a host device (such as a computer) in which the disc drive is mounted. The heads are mounted to a rotary actuator and are controllably positioned adjacent the tracks through the application of current to an actuator motor (such as a voice coil motor, VCM).
Present generation disc drives typically employ heads which utilize separate read and write elements. The write element typically has a thin-film inductive coil construction with a write gap placed in close proximity to the recording medium. Input data to be written to a disc are encoded and serialized to generate a series of bi-directional write currents which are applied to the write element. Each change in the polarity of the write current results in a magnetic flux reversal, or flux transition, in the recording medium. Data are thus recorded along each track at a selected frequency in relation to the presence of a flux transition (a logical 1) or the absence of a flux transition (a logical 0) at regular intervals along the track.
The read element is provided from a magneto-resistive (MR) material which is configured to exhibit changed electrical characteristics when subjected to a magnetic field of a selected orientation. During a read operation, the read element is biased using a relatively small bias current (or bias voltage), and the selective magnetization of the disc is detected in relation to induced changes in voltage across (or current through) the read element caused by the magnetization pattern along the track.
MR read elements typically have a semiconductor construction with very thin internal boundary areas and are thus extremely delicate and easily damaged. It is important to not stress a read element by dissipating too much power through the element, as such stress over time may lead to degraded performance and reduced operational life. The power rating of a read element provides an upper limit on the maximum read bias current magnitude that should be applied to the element during operation.
Disc drive manufacturers attempt to select appropriate read bias current magnitudes for each head that are well within the maximum limits that the heads can safely handle, and take steps to ensure that such limits are not exceeded during operation. For example, U.S. Pat. No. 6,141,165 issued to Nguyen et al. discloses a head switching operation in which a disc drive switches from a presently selected MR head to a target MR head. When the target head uses a larger bias current than the presently selected head, the drive switches to the target head and then increases the bias current. Contrawise, when the target head uses a smaller bias current than the presently selected head, the bias current applied to the presently selected head is reduced and then the drive switches to the target head. In this way, even temporary overstress conditions in either the presently selected head or the target head are eliminated.
While these and other prior art methodologies have been found to advantageously reduce the possibility of overstressing MR read elements, there are still conditions that may be encountered during drive operation that can lead to an overstress condition. With the continuing trend of providing disc drives with ever greater levels of data storage and data rate capabilities, it is contemplated that future generation heads will have ever increasing levels of reader sensitivity and will thus be even more prone to damage from overstress conditions. There is therefore a continued need for improvements in the art whereby such overstress conditions can be reduced or avoided, and it is to such improvements that the present invention is directed.
The present invention is directed to an apparatus and method for transferring data between a recording surface of a disc drive data handling system and a host device.
In accordance with preferred embodiments, the disc drive data handling system includes a disc having a data recording surface, and a read/write head having separate write and read elements used to write data to and transduce data from the recording surface. A communication channel is provided to direct the transfer of data between the recording surface and a host device, with the communication channel asserting a write gate signal in preparation of the writing of data.
A preamplifier driver circuit is configured to apply write currents to the write element to write data to the recording surface and to apply a first read bias signal of selected, nonzero magnitude to the read element to transduce data from the recording surface. In response to the write gate signal, the preamplifier driver circuit generates a second read bias signal of selected, nonzero magnitude different from the magnitude of the first read bias signal and applies the second read bias signal to the read element while applying the write currents to the write element. Upon deassertion of the write gate signal, the preamplifier driver circuit subsequently reapplies the first read bias signal to the read element to subsequently read data from the recording surface. Preferably, the first and second read bias signals comprise first and second read bias currents, respectively.
Moreover, the disc drive data handling system further comprises a servo circuit which controls the position of the read/write head in response to servo data stored in servo data fields on tracks on the recording surface. User data are written to user data fields interspersed between adjacent servo data fields. Thus, during a write operation in which user data are written to the user data fields, the preamplifier driver circuit applies the first read bias signal to the read element when the read/write head is disposed over the servo data fields, and applies the second read bias signal to the read element when the read/write head is disposed over the user data fields.
By reducing the read bias signal levels during the writing of data, the potential for damage due to cross-talk noise induced in the second read bias signal from magnetic coupling of the write element with the read element is greatly reduced.
These and various other features and advantages which characterize the present invention will be apparent from a reading of the following detailed description and a review of the associated drawings.